Parametric Design And Optimization Of Broadband Frequency Selective Surfaces Microwave Absorber

Frequency Selective Surface (FSS) microwave absorber is an important novel absorptive structural absorber, and has a broad scope in future application. Systematic and adequate methods of design and optimization will greatly push the development of FSS broadband absorber. Firstly, the loss mechanism and the parametric model of FSS broadband absorber are discussed in this paper. Secondly, the methods of performance evaluation, analysis and optimization are presented. Finally, by using the parametric model and the methods of evaluation and analysis, some FSS broadband absorbers are optimized and designed for different emphasis, such as geometry of unit cell pattern and arrangement of layers. The main contents are as follows:The absorption rationale of FSS absorber is discussed from point of view of resonance and impedance match. Based on transmission line equivalent circuit model, all kinds of parameters which affect the resonance and impedance matching state of FSS absorber are qualitatively analyzed. And then the method of parameterizing the FSS absorber model is given based on those design parameters, through taking the dimension of unit cell pattern, the electrical parameters of devices, and the parameters of structure layers into consideration.An effective method for evaluating the broadband performance of FSS absorber is discussed by its specific characteristics. By way of evaluation function, a method to describe two-dimension (2D) resolution space of FSS absorber is given. Genetic algorithm (GA) is analyzed and improved for optimizing parameter model of FSS absorber. Furthermore, based on the above method of design, evaluation, analysis, and optimization, a smart optimization framework for FSS absorber is put forward.A wideband switchable FSS absorber-reflector applied in4-8GHz is carried out. The switchable performance is designed and optimized with an emphasis in the parameters of pattern. A tunable unit cell pattern is designed based on coupled double split-rings. For comprehensive evaluating and optimizing the performances of switchable FSS in two opposite states, polymorphic union evaluation genetic algorithm (PUE-GA) is put forward for the first time. And finally strong absorption (-10dB) in OFF state and satisfied reflection in ON state are obtained in this switchable FSS wideband absorber.A tunable FSS absorber with dual-degrees of freedom (DOF) design aims to apply for1-5GHz is discussed. The tunable absorptive performance is systematically designed and optimized focus on the parameters of pattern. Based on a simple prototype unit cell resonator, an approach for achieving multi-resonances is investigated. And a unit cell pattern with gradient edges is extensively discussed. By loading tunable devices and designing suitable bias network, two operational DOF is provided for FSS absorber and is able to fully utilize its characteristic of multi-resonances. As a result, the tunable FSS absorber with dual-DOF has wideband absorption with the reflectivity below-10dB in the range of1-5GHz.A polarization-independent broadband tunable FSS absorber for the application of1-8GHz is investigated. The tunable absorptive performance is designed and optimized based on the dimension of pattern and the thickness of layers. After the above design of unit cell pattern with gradient edges, a simplified and improved polarization-independent basic pattern is designed, and the tunable and absorptive performances are maintained during this process. After optimization by using PUE-GA and loaded the bias network, the desired broadband tunable performance with-10dB reflection coefficient in1-8GHz is finally achieved.A polarization-independent broadband passive FSS absorber is studied and designed by using multi-layer structure focused on1-8GHz wideband absorptive performance. The passive absorptive performance is designed and optimized with an emphasis in the parameters of pattern and multi-layer structure. After relaxing the constraint condition of arrangement of multi-layer, more suitable conformation of FSS structure for1-8GHz application is searched. By using the framework of Designâ†'Global optimizationâ†'Analysisâ†'Local optimization, the performance of multi-layer FSS broadband absorber is optimized. The designed absorber has polarization-independent and broadband absorptive performance with-10dB reflection in1-8GHz. All the work of this dissertation shows that the method of parameterizing model and relative design, evaluation, analysis, and optimization tools are helpful to improve the design of active and passive FSS broadband microwave absorbers. These microwave absorbers all have good performances depending on their frequency bands. These research will lay the foundation for application of stealth technology fields.